1. Field of the Invention
The present invention relates to a method of manufacturing an electron source having an array of a plurality of electron-emitting devices, and manufacturing an image display apparatus using the electron source.
2. Description of the Related Art
Conventionally, two types of devices, namely hot and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction type emission devices, field emission type electron-emitting devices(to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, “Physical properties of thin-film field emission cathodes with molybdenium cones”, J. Appl. Phys., 47, 5248 (1976).
A known example of the MIM type electron-emitting devices is described in C. A. Mead, “Operation of tunnel-emission devices”, J. Appl. Phys., 32,646 (1961).
A known example of the surface-conduction type emission devices is described in, e.g., M. I. Elinson, “Radio E-ng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction type emission device utilizes the phenomenon that electrons are emitted from a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction type emission device includes electron-emitting devices using an Au thin film [G. Dittmer, “Thin Solid Films”, 9,317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, “IEEE Trans. ED Conf.”, 519 (1975)], a carbon thin film [Hisashi Araki et al., “Vacuum”, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 24 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction type emission devices. Referring to FIG. 24, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 24. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 24 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction type emission devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In the forming processing, for example, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the two ends of the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after the forming processing, electrons are emitted near the fissure.
The above surface-conduction type emission devices are advantageous because they have a simple structure and can be easily manufactured. For this reason, many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of surface-conduction type emission devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, electron sources, and the like have been studied.
As an application to image display apparatuses, in particular, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open No. 2-257551 filed by the present applicant, an image display apparatus using the combination of a surface-conduction type emission device and a fluorescent substance which emits light upon reception of electrons has been studied. This type of image display apparatus using the combination of the surface-conduction type emission device and the fluorescent substance is expected to have more excellent characteristics than other conventional image display apparatuses. For example, in comparison with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require a backlight because it is of a self-emission type and that it has a wide view angle.
The present inventors have examined surface-conduction type emission devices of various materials, various manufacturing methods, and various structures, in addition to the above-mentioned conventional surface-conduction type emission device. Further, the present inventors have made extensive studies on a multi electron source having a large number of surface-conduction type emission devices, and an image display apparatus using this multi electron source.
The present inventors have examined a multi electron source using an electrical wiring method shown in, e.g., FIG. 25. That is, a large number of surface-conduction type emission devices are two-dimensionally arranged in a matrix to obtain a multi electron source, as shown in FIG. 25.
Referring to FIG. 25, numeral 4001 denotes a surface-conduction type emission device; 4002, a row wiring; and 4003, a column wiring. The row and column wirings 4002 and 4003 actually have finite electrical resistances, which are represented as wiring resistances 4004 and 4005 in FIG. 25. This wiring method is called a simple matrix wiring method. For the illustrative convenience, the multi electron source is illustrated in a 6×6 matrix, but the size of the matrix is not limited to this. For example, in a multi electron source for an image display apparatus, a number of devices enough to perform a desired image display are arranged and wired.
In a multi electron source in which surface-conduction type emission devices are arranged in a simple matrix, appropriate electrical signals are applied to the row and column wirings 4002 and 4003 to output a desired electron beam. For example, to drive the surface-conduction type emission devices on an arbitrary row in the matrix, a selection voltage Vs is applied to the column wiring 4002 on the row to be selected, and at the same time, a non-selection voltage Vns is applied to the row wirings 4002 on unselected rows. In synchronism with this, a driving voltage Ve for outputting electrons is applied to the column wirings 4003. According to this method, when voltage drops across the wiring resistances 4004 and 4005 are neglected, a voltage (Ve−Vs) is applied to the surface-conduction type emission device on the selected row, and a voltage (Ve−Vns) is applied to the surface-conduction type emission devices on the unselected rows. When the voltages Ve, Vs, and Vns are set to appropriate levels, electrons having a desired intensity must be output from only the surface-conduction type emission device on the selected row. When different driving voltages Ve are applied to the respective column wirings, electrons having different intensities must be output from respective devices on the selected row. Since the surface-conduction type emission device has a high response speed, a time for outputting an electron beam can be changed by changing a time for applying the driving voltage Ve.
A multi electron source obtained by arranging surface-conduction type emission devices in a simple matrix has a variety of applications. For example, when a voltage signal corresponding to image information is appropriately applied, the multi electron source can be applied as an electron source for an image display apparatus.
The present inventors have made extensive studies for improving the characteristics of the surface-conduction type emission device to find that activation processing is effectively performed during the manufacture.
As described above, the electron-emitting portion of the surface-conduction type emission device is formed by processing (forming processing) of flowing a current through a conductive thin film to partially destroy or deform this thin film, thereby forming a fissure. If activation processing is performed subsequently, electron-emitting characteristics can be greatly improved.
In activation processing, the electron-emitting portion formed by the forming processing is electrified under appropriate conditions to deposit carbon or a carbon compound around the electron-emitting portion. Graphite monocrystalline, graphite polycrystalline, amorphous carbon, or mixture thereof is deposited to a thickness of 500 Å or less around the electron-emitting portion by periodically applying a voltage pulse in a vacuum atmosphere of 10−5 Torr. These conditions are merely an example and properly changed in accordance with the material and shape of the surface-conduction type emission device. This processing can increase the emission current at the same application voltage typically 100 times or greater the emission current immediately after forming processing. Note that the partial pressure of the organic substance in the vacuum atmosphere is desirably reduced after activation processing. For this reason, activation processing is desirably performed for each device in manufacturing a multi electron source formed by arranging a large number of surface-conduction type emission devices in a simple matrix.
The additional activation processing stabilizes the electron-emitting characteristics of surface-conduction type emission devices. However, the activation processing applied to multi surface-conduction type emission devices arranged in a simple matrix poses the following problems.
For example, surface-conduction type emission devices arranged in an m×n simple matrix are activated by applying a voltage every predetermined time in the order from the first to mth row wirings. An equivalent circuit in activating the electron-emitting devices arranged in a simple matrix is shown in FIG. 26. FIG. 26 shows the state in which an activation voltage waveform is applied to devices connected to the second row wiring.
FIG. 27 is a waveform chart showing the waveform of an application voltage signal in this activation processing. A voltage waveform having a pulse width T1, period T2, and voltage value Vf0 is applied. The activation time on each row wiring is determined from the activation characteristics of each device as shown in FIG. 28 or the like. Problems occur when devices arranged in a large matrix are activated in units of rows.
More specifically, a larger matrix size increases the influence of a voltage drop caused by the wiring resistance. Some devices cannot receive a sufficient voltage, which varies the electron-emitting characteristics of respective devices.
To give uniform electron-emitting characteristics to respective devices, a uniform voltage must be applied to the devices. However, a larger matrix size causes a larger voltage drop under the influence of the wiring resistance of a row wiring, so no predetermined voltage can be applied. In particular, a desired voltage cannot be applied to devices at almost the center of the row wiring. These devices cannot be satisfactorily activated, thus varying the characteristics of devices arranged in a matrix.
FIGS. 29A and 29B are graphs each schematically showing a voltage drop in matrix wiring. FIG. 29A schematically shows a voltage applied to each device when devices on the second row are activated at the voltage value Vf0 in an m×n simple matrix shown in FIG. 26. Reference symbol F(2,1) denotes a device on the second row and first column; F(2,2), a device on the second row and second column; and F(2,3), a device on the second row and third column. The abscissas in FIG. 29A represents the column number (pixel number). In FIG. 29A, since a voltage is applied from the two sides of the row wiring, as shown in FIG. 26, the voltage drop is the largest on the kth column at almost the center, and the voltage value applied to the device F(2,k) is Vfk (<Vf0). That is, this device receives only a voltage value smaller than the voltage Vf0 to be applied by Vfdf (=Vf0−Vfk).